Circuit for food mixer

ABSTRACT

An alternating current electric motor speed control circuit including a bi-directional semiconductor control element in the motor circuit triggered from a blocking to a conductive state by the application of a potential to its control electrode applied through governor contacts of a motor speed governor contacts, which contacts are closed when the motor speed drops below a particular value which can be varied and which carry a small proportion of the total motor current.

United States Patent Collie A [s41 CIRCUITFOR FOOD MIXER Inventor:

Arthur A. Collie, Hayling island,

- England Assignee: Kenwood Manufacturing (Working) Limited, Hampshire, England Filed: June 23,1971

Appl.No.: 156,038. I v

Related us. Application om Continuation ofSer. NO. 812,002, April 1, r 1969, abandoned,

us Cl. ..318/325, 313/345, 318/397 rm.c|....- ..,.....'H02 s/0s Field of Search..'.... 3l8/ 22 7, 325, 327, 331, 34s, v v 313/397 References Cited UNITED- STATES PATENTS 12/1965 Seileret a1,. .,.,.318/325 [s71 g I An alternating current electric motor speed control [451 Oct. 31, 1972 l2ll968 Morgan et al. ..32l/43 3,238,434' 3/1966 Blitzetal "313/323 3,242,409 3/1966 Edwards ..31s/325 9/1969 Steele ..'.313/227 Primary Examiner-Gene Z. Rubinson Attorney-Stevens, Davis, Miller & Mosher ABSTRACT circuit including a bi-directional semiconductor control element in the motor circuit triggered froma blocking toa conductive state by the application of a potential to its control electrode applied through govem'or contacts of a motor speed governor contacts, which contacts are closed when the motor speed drops below a particular value which can be varied and which carry a small proportion of the total motor current.

v v 4 Claims, 3 Drawing Figures l 1 CIRCUIT FOR FOODMIXER:

This application is a continuation of Ser. ,No.

812,002, filed Apr. 1', I969 andnow abandoned.

This invention relates to an alternating current elec tric motor control circuit.

. I It is known to control the speed of an electric motor by means of a governor having electric contacts connected in the motor control circuit and "rotated with the armature of the motor so that when the speed of the motor exceeds a given value the contacts are open and the speed of the motor is reduced. This arrangement suffers from the disadvantage that the contacts carry the full load of the motor current and are'therefore subject to considerable wear. a t According to the present invention there is provided ,an'alter'nating current electric motor control circuit in- 1 cludinga bi-directionalsemiconductor control-element in the motor circuit',-a gate or control electrode of the element con'nected to governor contacts of a motor speed governor, so that the conductivity of the element is varied according to whether the governor contacts are open or closed and a series combination of an electrically resistive element and a'capacitive reactive element connected in parallel with the semiconductor control element.

In order that theinvention may be more clearly uni a motor armature 1 connected in series" with a, bi-

directional semiconductor control element 2, field windings 3 and4, and interference suppression chokes 5 and 6 acrossa pair of supply terminals 7 and 8. A

' control switch 9 is connected between the choke 5 and I I 40 previously, since the limitation imposed by the burning the field winding 3 and the fixed contact of the switch-'9.

is earthed via a 0.01 microfarad capacitor 10 and'connected to the junction between the choke 6 and a field winding 4 via a 0.1 r'nicrofarad capacitor 1 I. Across the element 2 there is connected a resistor R1 inseries with a capacit'orFCl. The'resistor R1 is of the order of 100 ohms and" the capacitor C1 of the order of 0.1- microfarads. The junction of the resistor R1 and the capacitor C1 is connected via a pair of governor contacts for the motor and a-resistor R2 to the control electrode of the element 2.

FIG. 2 shows a circuit including all the elements of FIG. 1, but with the variation that the current through the governor contacts 15 does not pass through the resistor R1. v

The bi-directional semiconductor control element is and in reverse directions. Suitable elements are known commercially as Triacs. I

Thus by suitably proportioning the circuit including the resistor R1 and the capacitor C1 it is possible to apply a triggering voltage to the control electrode of the element 2 every time that the governor contacts 15 close.

a bi-directional triode thyristor which may be triggered 1 semiconductor control rectifiers connected in parallel In operation it isarranged that the governor contacts 15" are-closed when the motor is rotating at normal speedsv and that these contacts are opened when the motor speed exceeds a given value. As illustrated in FIG; 3.of the accompanying drawings, the governor consists of weights fixed toiflexible members 21, so

that the weights are displaced-further from the axis of the motor as the motor speed increases, and-a ball bearposition of the contacts 15- can be'variedfrom outside the motor, as they aresupported on a contact bearing plate which .can be moved by asnail cam arrangement consistingofa pin 26 attached tothe plate 25and inserted in a groove 28 in a head 27 which is rotatable. As the groove 28 is not circular, pin 26 and plate 25 20 move parallel tothe motor axis when the-head 27 is I rotated. Each position of the plate 25 defines a motor speedat which the contacts 15 will be separatedby the ballbearing 2 When the contacts open the element 2 reverts to a 2 blocking state at the next reversal of the supply current,

' that is when the current through the element and themotor falls below the holding; current for the element,

- and thefspeed of the motor automatically falls. When the motor speed falls below the given value the governor contacts 15 closeand the potential applied to the control electrode of the element 2 causes the element to conduct and the mean motor speed to be main-' tained.

There is thus provided an arrangement in which the The arrangement is suitable for use in controlling the I speed of motors insuch appliances as food mixers and sewing, machines. In the latter case aremote control may be providedto control the setting of the contacts which governs the speed of the motor. The arrangement may also be used .in controlling speed of motors in hand held appliances or tools.

I I claim:

I 1. In an alternating current electric motor control circuit comprising, in combination:

a. an alternating current electric motor including an armature and first and second field windings coupled in series one on each side of said armature,

b. an alternating current motor supply circuit coupled to said first and second field windings, and.

c. a motor speed governor having a pair of contacts separable in response to the speedof said motor exceedingagiven value,

the improvement comprising: I o

d. a bi-directional triode thyristor coupled in series between said first field winding and said armature, said thyristor having a control'electrode coupled to one of said pair of contacts,

f. the other of said pair of contacts being coupled to the conductive path between said first field winding and said thyristor.

2. An electric motor control circuit as defined in claim 1, in which said other of said pair of contacts is connected to a junction of said resistive element and said capacitive reactive element. r

3. An electric motor control circuit as defined in claim 1, further comprising first and second interference suppression chokes coupled in series with said first and second field windings, respectively, and said electric motor supply circuit.

4. In an alternating current electric motor control circuit comprising, in combination:

a. an alternating current electric motor including an armature and first and second field windings coupled in series one on each side of said armature,

b. an alternating current motor supply circuit coupled to said first and second field windings, and

c. improvement comprising: motor speed governor having a pair of contacts separable in response to the speed of said motor exceeding a given value,

the improvement comprising: f d. a bi-directional triode thyristor coupled in series between said first field winding and said armature,

said thyristor having a control electrode con to one of said pairof contacts, I e. an electrical resistive elementand a capacitive reactive element connected in series with each other and in parallel with said thyristor,

pled

f. a further resistive element connected in series between said one of said pair of contacts and said control electrode,

g. the other of said pair of contacts being coupled in one on each side of said motor, i. capacitor means connected in parallel with said motor and in series with said choke means; and j. switch means in that part of said motor supply circuit which is in parallel with said capacitor means. 

1. In an alternating current electric motor control circuit comprising, in combination: a. an alternating current electric motor including an armature and first and second field windings coupled in series one on each side of said armature, b. an alternating current motor supply circuit coupled to said first and second field windings, and c. a motor speed governor having a pair of contacts separable in response to the speed of said motor exceeding a given value, the improvement comprising: d. a bi-directional triode thyristor coupled in series between said first field winding and said armature, said thyristor having a control electrode coupled to one of said pair of contacts, e. an electrical resistive element and a capacitive reactive element connected in series with each other and in parallel with said thyristor, and f. the other of said pair of contacts being coupled to the conductive path between said first field winding and said thyristor.
 2. An electric motor control circuit as defined in claim 1, in which said other of said pair of contacts is connected to a junction of said resistive element and said capacitive reactive element.
 3. An electric motor control circuit as defined in claim 1, further comprising fiRst and second interference suppression chokes coupled in series with said first and second field windings, respectively, and said electric motor supply circuit.
 4. In an alternating current electric motor control circuit comprising, in combination: a. an alternating current electric motor including an armature and first and second field windings coupled in series one on each side of said armature, b. an alternating current motor supply circuit coupled to said first and second field windings, and c. a motor speed governor having a pair of contacts separable in response to the speed of said motor exceeding a given value, the improvement comprising: d. a bi-directional triode thyristor coupled in series between said first field winding and said armature, said thyristor having a control electrode coupled to one of said pair of contacts, e. an electrical resistive element and a capacitive reactive element connected in series with each other and in parallel with said thyristor, f. a further resistive element connected in series between said one of said pair of contacts and said control electrode, g. the other of said pair of contacts being coupled in the conductive path between said first field winding and said thyristor, h. two interference suppression choke means, coupled in series in said electric motor supply circuit, one on each side of said motor, i. capacitor means connected in parallel with said motor and in series with said choke means; and j. switch means in that part of said motor supply circuit which is in parallel with said capacitor means. 